A radial extended interaction oscillator has been presented in this paper. This new structure has characteristics such as compact structure, good heat dissipation and high output power. The characteristics trends of 4-cavities radial EIO has been determined through the analysis of a single coaxial resonator gap. And the operating frequency and voltage is more accurately tested by simulation of electromagnetic simulation software and small signal theory analysis. Since the electron emission surface of the electron gun of radial EIO is much larger than that of conventional EIO, so in the case of small current density, a large current can be obtained. When the voltage is 5kV and the current is 8.48A, the PIC simulation shows that the radial EIO could generate 2.6 kW in 30.011 GHz.